Our invention pertains to an ignition system for multicylinder, spark-ignition, internal-combustion engines such as those for motor vehicles, and more specifically to improvements in an ignition system of the type having no rotary switch known as the ignition distributor.
An ignition system has been suggested which dispenses with the usual distributor (shown in FIG. 1 of the drawings attached hereto). The known distributorless ignition system incorporates, instead of the distributor, rectifying diodes connected between the secondary winding of an ignition coil or transformer and respective spark plugs. As voltages are induced in the secondary winding in its opposite directions in timed relation with the revolutions of the engine crankshaft, the diodes function to cause the spark plugs to ignite the compressed charges in the cylinder combustion chambers in a prescribed sequence.
The omission of the distributor with its mechanical contacts offers the advantage of no interference noise production. However, abnormally high or abrupt voltages that almost inevitably develop in the system have been easy to degrade or destroy the rectifying diodes. These diodes have had to be of construction well withstanding such overvoltages. If the discharge voltage of the spark plugs ranges between 10 and 25 kilovolts (kV), for example, then the rated maximum (peak) total reverse voltage V.sub.RM of the diodes has had to be more than 45 kV. (Actual breakdown voltage is considerably higher than V.sub.RM.)
Such high voltage diodes normally take the form of laminated diode chips. Usually the breakdown voltage of each diode chip has been set at 1000 V or more in order to reduce the number of laminated chips to a minimum from an economic point of view. Even if the V.sub.RM of the diodes is made about 45 kV, their properties have been easy to deteriorate unless sufficient measures are taken against destruction.
Thus the conventional distributorless ignition system could be relied upon for satisfactory performance in actual use only when the rectifying diodes were made capable of withstanding overvoltages far above the normal range in which they were intended to operate. Such diodes are of course very costly. The diodes and other pertinent parts of the ignition system must further be sufficiently insulated against the possible excessive overvoltages. For all these reasons the prior art system has failed to find widespread acceptance.